Bragg mirrors called omnidirectional dielectric reflectors (ODRs), have recently been used as claddings for hollow fibers and integrated waveguides. In addition, gold-terminated ODR cladding mirrors, and their fabrication (by a self-assembly buckling process), has been described elsewhere.
In conventional total internal reflection waveguides, input/output couplers based on mode cutoff in a taper were proposed and demonstrated in the 1970s. However, these couplers were not widely used for at least two reasons. First, the fabrication of planar waveguides with vertically tapered core thickness is not trivial. Second, it is necessary to orient the free-space beam along a nearly in-plane direction (i.e. parallel to the substrate), since mode cutoff occurs at the critical angle for total internal reflection between the core and one of the cladding materials. More recently, surface-normal coupling in symmetric hollow-core waveguides with Bragg reflector claddings was proposed but not experimentally demonstrated.